Electromagnetic fuel injectors used in internal combustion engines control the discharge of precisely metered quantities of fuel to the engine combustion chambers. Proper control of the shape of fuel discharge results in low exhaust emissions, high fuel economy, and improved driveability performance.
A typical electromagnetic fuel injector includes a solenoid assembly disposed in a generally cylindrical shell defined by a longitudinal axis having a fuel inlet at an upstream end and a nozzle at a downstream end. A reciprocally moveable valve assembly, mounted for linear movement along the longitudinal axis, has a valve end which is adapted to be moved from a seated and fuel sealing position with a cooperating valve seat and seat orifice therethrough, to an open position to define a fuel flow passage through the nozzle. The valve assembly is controlled in its movement by the electromagnetic force of the solenoid assembly, as is known in the art.
A flow director plate sub-assembly, positioned immediately downstream of the valve seat and seat orifice and supported in a fixed position adjacent the nozzle, typically comprises a plate member and a cup-shaped director plate retainer. The plate member has one or more orifices, located at predetermined angles and orientations relative to the longitudinal axis of the solenoid assembly, for targeting and controlling the spray pattern of fuel metered by the valve seat. The plate member typically also includes a circumferential flange. The plate member is held in proper position by the cup shaped director plate retainer which is pressed into a cylindrical recess at the injection end of the injector. The circumferential flange of the plate member cooperates with a nozzle shoulder to position the plate member coaxially with the valve seat.
In the prior art, the relatively large depth of the recess and the relatively large diameter of the recess at the injector tip in comparison to the diameter of the valve seat orifice are desirable for hot fuel handling and for minimizing plugging of the flow director orifice. Unfortunately, the large diameter and depth of the recess downstream of the valve seat also permit metered fuel to accumulate in the recess and to be released toward the combustion chamber during the next injector actuation as a non-controlled and non-atomized droplet. This is undesirable because such a droplet can fail to vaporize completely and cause an over-enrichment of delivered fuel, thereby causing an increase in engine hydrocarbon emissions, unstable engine speed and a reduction in fuel efficiency.
Therefore, what is needed in the art is a means for reducing the accumulation of a fuel drip downstream of the valve seat and a means for eliminating fuel dripping.